Drive system and control method for chuck device

ABSTRACT

A drive system for driving a chuck device includes a controller and a switching valve, which is a 5-port servo valve, switching the state of supply of compressed air to the chuck device based on a valve command signal from the controller. During switching of first and second fingers from a closed position to an open position, when the axial position of a piston reaches a switch point, which is a predetermined distance short of a target position corresponding to a freely selected intermediate position of the first and second fingers, the switching valve is opened at a third opening for a predetermined period and then switched to be opened at a fourth opening so that supply and discharge of compressed air are stopped. As a result, the first and second fingers stop in the intermediate position.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2019-098747 filed on May 27, 2019, thecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to drive systems and control methods forchuck devices capable of gripping workpieces via fingers that can beopened and closed.

Description of the Related Art

Chuck devices gripping and releasing workpieces under the effect ofsupply of air have been used for, for example, carrying the workpieces.As disclosed in Japanese Patent No. 3932392, the inventors have proposeda chuck device capable of gripping and releasing workpieces by openingand closing gripping members as a piston disposed inside a chuck body isdisplaced under the effect of supply of compressed air.

In the chuck device, when compressed air is supplied to the inside ofthe chuck body to move the piston toward an end member, levers engagedwith the leading end of the piston rotate, and the gripping membersengaged with the leading ends of the respective levers approach eachother. As a result, the chuck device enters a gripping state where thechuck device can grip a workpiece. At this moment, the displacement ofthe piston is restricted by the piston brought into contact with the endmember, and the gripping members are kept at a predetermined grippingposition.

On the other hand, when compressed air is supplied to a space on a sideopposite to the above in the chuck body, the piston moves in a directionaway from the end member, and thereby the levers rotate in directionsopposite to the above. As a result, the gripping members are separatedfrom each other and enters a release state.

Moreover, in the chuck device, the end member is screwed into the upperend of the chuck body, and the position of the end member along theaxial direction can be adjusted. To adjust the gripping position of thegripping members, the axial position of the end member is adjusted byrotating the end member. This limits the amount of stroke of the pistonalong the axial direction and thereby adjusts the amount of movement ofthe gripping members in directions along which the gripping membersapproach each other. In this manner, the gripping position is adjustedfrom a predetermined position.

SUMMARY OF THE INVENTION

However, in the above-described chuck device, the adjustable amount ofmovement of the gripping members (the adjustable amount of stroke of thepiston) to adjust the gripping position is limited to the movabledistance of the end member along the axial direction. In addition, sincean operator performs the adjustment by rotating the end member, theadjustment work is complicated, and the positioning with high precisionis difficult to achieve. Moreover, there is a demand to make adjustmentsto the amount of movement of the gripping members and to select the openor closed state of the gripping members using an electrical signal froma higher level controller.

A general object of the present invention is to provide a drive systemand a control method for a chuck device capable of stopping fingersserving as gripping members at any position easily and with highprecision.

According to an aspect of the present invention, provided is a drivesystem for driving a chuck device including a piston displaceable in anaxial direction under an effect of supply of fluid and a pair of fingersconfigured to be opened and closed according to the displacement of thepiston, the drive system comprising:

a controller;

a detection sensor configured to detect an axial position of the piston;and

a switching valve configured to switch a state of supply of the fluid tothe chuck device,

wherein the switching valve is a servo valve, of which degree of valveopening is controllable based on a control signal input from thecontroller, and an amount of displacement of the piston and an amount ofopening and closing of the fingers are controlled by changing the degreeof valve opening.

According to the present invention, the chuck device includes the pistondisplaced in the axial direction by the fluid supplied to the chuckdevice and the pair of fingers opened and closed according to thedisplacement of the piston. The drive system including the chuck deviceincludes the detection sensor configured to detect the axial position ofthe piston and the switching valve configured to switch the state ofsupply of the fluid to the chuck device. The switching valve is a servovalve of which degree of valve opening can be controlled based on thecontrol signal input from the controller, and the amount of displacementof the piston and the amount of opening and closing of the fingers canbe controlled by changing the degree of valve opening.

Thus, the degree of valve opening can be controlled by inputting thecontrol signal to the switching valve made of the servo valve, and thedirection and amount of displacement of the piston can be controlled byswitching the state of supply of the fluid to the chuck device.Consequently, the amount of opening and closing of the pair of fingerscan be easily controlled.

As a result, the fingers can be stopped at any position easily and withhigh precision by freely switching the switching valve using the controlsignal from the controller compared with the known chuck device thatrequires the operator to move the end member provided for the chuck bodyin the axial direction by rotating and thereby to adjust the amount ofstroke of the piston so that the gripping members are stopped at afreely selected position.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which a preferredembodiment of the present invention is shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic circuit diagram illustrating a drive system for achuck device according to an embodiment of the present invention;

FIG. 2 is an overall cross-sectional view of the chuck deviceconstituting the drive system in FIG. 1;

FIG. 3 is a schematic circuit diagram of the drive system in FIG. 1 whena switching valve is switched from a first switch position to a secondswitch position to change a gripping portion to a release state;

FIG. 4 is a schematic circuit diagram of the drive system in FIG. 1 whenthe switching valve is switched to a third switch position to change thegripping portion to a gripping state;

FIG. 5 is a diagram of characteristic curves illustrating therelationships between a valve command signal to the switching valve andthe supply rate, the discharge rate, and the valve opening in the drivesystem in FIG. 1;

FIG. 6 is a time chart illustrating the relationships between time and acommand signal to a controller, the valve command signal from thecontroller to the switching valve, and a piston position signal in thedrive system in FIG. 1;

FIG. 7 is a schematic circuit diagram of a drive system obtained byproviding a pair of pressure sensors capable of detecting the pressuresin a head-side cylinder chamber and a rod-side cylinder chamber for thedrive system in FIG. 1;

FIG. 8 is a schematic circuit diagram of a drive system obtained byproviding a differential pressure sensor capable of detecting thedifference between the pressure in the head-side cylinder chamber andthe pressure in the rod-side cylinder chamber for the drive system inFIG. 1; and

FIG. 9 is a schematic circuit diagram illustrating a drive system forthe chuck device according to a modification, the drive system includinga pair of switching valves.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated in FIG. 1, a drive system 10 for driving a chuck device12 according to an embodiment of the present invention is applied to thechuck device 12 opening and closing under the effect of supply ofcompressed air and includes a switching valve 14 switching a state ofsupply of compressed air (fluid) to the chuck device 12 and a controller16 outputting a valve command signal (control signal) to the switchingvalve 14 based on an input command signal. Moreover, the drive system 10selectively connects first and second ports 66 and 70 (described below)to first and second body ports 36 and 38 (described below),respectively, of the chuck device 12 through the switching action of theswitching valve 14. In addition, the controller 16 stores a control mapfor driving the chuck device 12 in advance.

First, the configuration of the chuck device 12 will be described withreference to FIGS. 1 and 2.

The chuck device 12 includes a tubular chuck body 18, a piston 20disposed inside the chuck body 18 to be freely displaced, a grippingportion 30 including a pair of first and second fingers 26 and 28 thatopen and close via levers 24 a and 24 b, respectively, engaged with arod part 22 of the piston 20, and a detection sensor 32 disposed on aside part of the chuck body 18 to detect the position of the piston 20.The chuck device 12 described above is an air chuck opening and closingunder the effect of supply of compressed air.

The chuck body 18 has, for example, a substantially rectangularcross-section. The chuck body 18 has a body hole 34 passing through thechuck body 18 in the axial direction (directions of arrows A and B) andthe first and second body ports 36 and 38 opened in a side surface andcommunicating with the body hole 34 to supply and discharge pressurizedfluid.

The body hole 34 is opened in one end part of the chuck body 18 andclosed by a head cover 40 fitted in the body hole 34. The head cover 40is held by a stop ring 42 while being engaged with a stepped part of thebody hole 34, and the movement of the head cover 40 toward the open oneend part (in the direction of the arrow A) is restricted by the stopring 42.

The body hole 34 is partitioned into a head-side cylinder chamber(cylinder chamber) 44 (described below) formed between the piston 20 andthe head cover 40 and a rod-side cylinder chamber (cylinder chamber) 46defined between the piston 20 and another end part of the chuck body 18.

The first and second body ports 36 and 38 are separate from each otherin the axial direction of the chuck body 18 (in the directions of thearrows A and B) by a predetermined distance. The first body port 36communicates with the head-side cylinder chamber 44, and the second bodyport 38 communicates with the rod-side cylinder chamber 46. The firstand second body ports 36 and 38 are connected to the first and secondports 66 and 70 (described below) of the switching valve 14 via firstand second tubes 68 and 72, respectively, so that compressed air issupplied and discharged through the switching action of the switchingvalve 14.

On the other hand, a plate-like base body 48 is joined to the other endpart of the chuck body 18 to be substantially orthogonal to the axis ofthe chuck body 18 and thus closes the other end part. The base body 48has a pair of insertion holes 49 a and 49 b in which the levers 24 a and24 b are partially fitted.

Moreover, a rail groove 50 is formed in the base body 48 so that thepair of first and second fingers 26 and 28 constituting the grippingportion 30 are guided to be freely displaced along the rail groove 50.The rail groove 50 is formed in a side surface of the base body 48 on aside opposite the side on which the chuck body 18 lies, and linearlyextends in a longitudinal direction (in a direction of an arrow C inFIG. 2) substantially orthogonal to the axis of the chuck body 18.

The piston 20 can be displaced in the axial direction (in the directionsof the arrows A and B) such that, for example, the outer circumferentialsurface can slide along the inner circumferential surface of the bodyhole 34. A piston packing 52 attached to the outer circumferentialsurface is in contact with the inner circumferential surface, and amagnet 54 is disposed adjacent to the piston packing 52.

The detection sensor 32 attached to the side surface of the chuck body18 detects the magnetism of the magnet 54 and outputs the results in theform of an electrical signal to the controller 16. The axial positionand the displacement speed of the piston 20 along the axial direction(along the directions of the arrows A and B) are calculated from theoutput.

Moreover, one end face of the piston 20 faces the head cover 40 insidethe body hole 34, and another end face is provided with the rod part 22having a reduced diameter and extending toward the base body 48 (in thedirection of the arrow B). A damper 55 composed of an elastic materialis attached to a border region between the rod part 22 and the other endface. The rod part 22 is fitted in a rod hole 56 having a smallerdiameter than the body hole 34, and the leading end is provided with alink pin 58 orthogonal to the axial direction of the rod part 22. Thepair of levers 24 a and 24 b are rotatably engaged with the leading endof the rod part 22 via the link pin 58.

The levers 24 a and 24 b having a substantially L-shaped cross-sectionare paired with each other and disposed to be symmetric with respect tothe axis of the piston 20. The levers 24 a and 24 b are rotatablysupported by support shafts 60 a and 60 b provided for the chuck body 18and respectively fitted in bent, substantially middle parts of thelevers 24 a and 24 b.

Moreover, first end parts of the levers 24 a and 24 b respectivelyengaged with the link pin 58 via semicircular notches 25 a and 25 b, andsecond end parts 27 a and 27 b having a deformed cross-section andexpanding into a spherical shape are respectively fitted and held inengagement holes 61 a and 61 b in the first and second fingers 26 and 28constituting the gripping portion 30.

That is, the first end parts of the pair of levers 24 a and 24 b move inthe axial direction under the effect of displacement of the piston 20(the rod part 22) along the axial direction (along the directions of thearrows A and B) via the link pin 58, and as a result of this, the secondend parts 27 a and 27 b respectively rotate on the support shafts 60 aand 60 b to approach or be separated from each other. The grippingportion 30 includes the pair of first and second fingers (fingers) 26and 28 capable of being displaced along the rail groove 50 of the basebody 48. The first and second fingers 26 and 28 respectively includeblock-like body parts 62 a and 62 b guided along the rail groove 50 andclaw parts 64 a and 64 b respectively protruding from the body parts 62a and 62 b to be substantially orthogonal to the body parts to grip aworkpiece.

The first and second fingers 26 and 28 are disposed to be movable toapproach and be separated from each other along the rail groove 50 ofthe base body 48. In this case, the first finger 26 and the secondfinger 28 move symmetrically with respect to the axis of the piston 20.

Next, the configuration of the switching valve 14 will be described withreference to FIGS. 1, 3, and 4.

The switching valve 14 is, for example, a 5-port servo valve including avalve element (not illustrated) that opens and closes in response to thevalve command signal from the controller 16. The first port 66 isconnected to the first body port 36 of the chuck device 12 via the firsttube 68, and the second port 70 is connected to the second body port 38via the second tube 72.

Moreover, in the switching valve 14, a supply port 74 is connected to anair supply source (supply source) 78 supplying compressed air via athird tube 76, and first and second exhaust ports 80 and 82 communicatewith the outside.

When the switching valve 14 is in a first switch position P1 asillustrated in FIG. 1, the first and second ports 66 and 70 are notconnected to any of the supply port 74 and the first and second exhaustports 80 and 82. Thus, the switching valve 14 blocks supply ofcompressed air from the air supply source 78 to the chuck device 12 anddischarge of compressed air from the chuck device 12, bringing the chuckdevice 12 to a standstill.

When the switching valve 14 is switched to a second switch position P2as illustrated in FIG. 3 in response to the valve command signal, thesupply port 74 communicates with the first port 66, and thus the airsupply source 78 connected to the supply port 74 communicates with thefirst body port 36 of the chuck device 12. As a result, compressed airis supplied to the head-side cylinder chamber 44. At the same time, thesecond port 70 communicates with the second exhaust port 82, and thusthe second body port 38 of the chuck device 12 communicates with theoutside.

When the switching valve 14 is switched to a third switch position P3 asillustrated in FIG. 4 in response to the valve command signal, the firstport 66 communicates with the first exhaust port 80, and thus the firstbody port 36 of the chuck device 12 communicates with the outside. Atthe same time, the supply port 74 communicates with the second port 70.As a result, the air supply source 78 communicates with the second bodyport 38 of the chuck device 12, and compressed air is supplied to therod-side cylinder chamber 46.

That is, the switching valve 14 described above can be freely andsequentially switched between the first switch position P1, the secondswitch position P2, and the third switch position P3 in response to thevalve command signal input from the controller 16 based on, for example,a command voltage serving as the command signal. Specifically, theswitching valve 14 is switched to the second switch position P2, thefirst switch position P1, and the third switch position P3 in this orderas the value of the valve command signal gradually increases asillustrated in FIG. 5. The valve command signal is a signal forinputting, for example, timings of gripping or releasing and the amountof opening (amount of movement) of the first and second fingers 26 and28 to the controller 16.

The drive system 10 for the chuck device 12 according to the embodimentof the present invention is basically configured as above. Next, theoperations and operational effects thereof will be described. In thedescription below, a state where the switching valve 14 is in the firstswitch position P1 as illustrated in FIG. 1 is defined as an initialstate.

To change the gripping portion 30 of the chuck device 12 from theinitial state to a release state (open), the command signal indicatingto change the gripping portion 30 to the open state is input to thecontroller 16, and the valve command signal is input from the controller16 to the switching valve 14 to move the valve element (notillustrated). This causes the switching valve 14 to be switched to thesecond switch position P2 in which the supply port 74 is connected tothe first port 66 while the second port 70 is connected to the secondexhaust port 82 as illustrated in FIG. 3.

As a result, compressed air from the air supply source 78 is supplied tothe first body port 36 of the chuck device 12 through the first tube 68after flowing through the third tube 76, and the supply port 74 and thefirst port 66 of the switching valve 14.

Then, the piston 20 of the chuck device 12 is pushed by the compressedair supplied from the first body port 36 to the head-side cylinderchamber 44 and moves toward the other end part (in the direction of thearrow B) along the chuck body 18. As the piston 20 moves, the compressedair in the rod-side cylinder chamber 46 is discharged from the secondbody port 38 through the second tube 72 and from the second port 70 ofthe switching valve 14 to the outside through the second exhaust port82.

The movement of the piston 20 toward the other end part (in thedirection of the arrow B) causes the pair of levers 24 a and 24 bengaged with the rod part 22 to rotate respectively on the supportshafts 60 a and 60 b such that the second end parts 27 a and 27 b areseparated from each other. As a result, the first and second fingers 26and 28 move outward along the rail groove 50 to be separated from eachother, and enter the release state.

Moreover, the magnetism of the magnet 54 attached to the piston 20 isdetected by the detection sensor 32 disposed on the chuck body 18 and isoutput to the controller 16 as a position signal. This enables the axialposition of the piston 20 along the axial direction to be determined.Thus, based on the position of the piston 20, it is determined that thefirst and second fingers 26 and 28 are in an open position (releasestate; open) where the first and second fingers 26 and 28 are separatedfrom each other.

In this case, the piston 20 is displaced until coming into contact withan end part of the body hole 34, and then stops. The amount of outwardmovement (the amount of opening) of the first and second fingers 26 and28 corresponds to the axial position of the piston 20.

Next, how the gripping portion 30 including the first and second fingers26 and 28 in the above-described release state is switched to a grippingstate where the gripping portion 30 grips a workpiece or the like willbe described.

First, the command signal indicating to change the gripping portion 30to a closed state is input to the controller 16, and the valve commandsignal is input from the controller 16 to the switching valve 14 to movethe valve element (not illustrated). This causes the switching valve 14to be switched to the third switch position P3 in which the supply port74 is connected to the second port 70 while the first port 66 isconnected to the first exhaust port 80 as illustrated in FIG. 4.

As a result, supply of compressed air from the air supply source 78 tothe first body port 36 stops while the compressed air is supplied to thesecond body port 38 of the chuck device 12 through the second tube 72after flowing through the supply port 74 and the second port 70 of theswitching valve 14.

Then, the piston 20 of the chuck device 12 is pushed by the compressedair supplied from the second body port 38 to the rod-side cylinderchamber 46 and moves toward the one end part (in the direction of thearrow A) along the chuck body 18. As the piston 20 moves, the compressedair in the head-side cylinder chamber 44 is discharged from the firstbody port 36 through the first tube 68 and from the first port 66 of theswitching valve 14 to the outside through the first exhaust port 80.

The movement of the piston 20 toward the one end part (in the directionof the arrow A) causes the pair of levers 24 a and 24 b to rotaterespectively on the support shafts 60 a and 60 b such that the secondend parts 27 a and 27 b approach each other. As a result, the first andsecond fingers 26 and 28 move inward along the rail groove 50 toapproach each other. Thus, the gripping portion 30 enters the grippingstate where the gripping portion 30 can grip a workpiece (notillustrated) disposed between the claw part 64 a of the first finger 26and the claw part 64 b of the second finger 28.

Moreover, the magnetism of the magnet 54 attached to the piston 20 isdetected by the detection sensor 32 and is output to the controller 16as the position signal. As a result of this, the axial position of thepiston 20 is determined, and at the same time, it is determined that thefirst and second fingers 26 and 28 are in a closed position (grippingstate; closed) where the first and second fingers 26 and 28 are close toeach other.

In this case, the piston 20 moves toward the head cover 40 until thefirst and second fingers 26 and 28 grip the workpiece or until the firstand second fingers 26 and 28 come into contact with each other.

Next, how the gripping portion 30 including the first and second fingers26 and 28 is stopped at a freely selected intermediate position betweena release position and a gripping position will be described withreference to FIGS. 5 and 6. In the description below, the first andsecond fingers 26 and 28 are moved from the closed position (grippingstate) and stopped in the intermediate position.

FIG. 5 described above is a diagram of characteristic curvesillustrating the relationships between the valve command signal from thecontroller 16 to the switching valve 14 and the state of supply anddischarge of compressed air at the first and second ports 66 and 70. InFIG. 5, a characteristic curve F1 drawn with a solid line illustratesthe state of supply and discharge of compressed air to and from thefirst port 66 (the first body port 36), and a characteristic curve F2drawn with a broken line illustrates the state of supply and dischargeof the compressed air to and from the second port 70 (the second bodyport 38). That is, the state of supply and discharge of compressed airto and from the first port 66 and the flow rate (opening) changeaccording to the value of the valve command signal. The same applies tothe second port 70.

First, the command signal indicating to change the gripping portion 30to the closed state is input to the controller 16, and the valve commandsignal indicating to open the switching valve 14 at a first opening Vais input to the switching valve 14 based on the command signal. Thiscauses the switching valve 14 to be switched to the third switchposition P3 and thus causes the first and second fingers 26 and 28 to beplaced in the closed position. The axial position of the piston 20 isdetected by the detection sensor 32 and is input to the controller 16 asthe position signal. As a result, it is determined that the first andsecond fingers 26 and 28 are in the closed position.

As can be understood from FIG. 5, in the third switch position P3, theopening of the first port 66 and the opening of the second port 70 at apredetermined value of the valve command signal are identical to eachother, and the flow rate of compressed air discharged from the chuckdevice 12 through the first port 66 (the characteristic curve F1) andthe flow rate of compressed air supplied to the chuck device 12 throughthe second port 70 (the characteristic curve F2) are substantiallyidentical to each other.

Next, the command signal indicating to change the gripping portion 30from the closed state to the release state is input to the controller16, and the valve command signal based on the command signal is inputfrom the controller 16 to the switching valve 14. This causes theswitching valve 14 to be switched to the second switch position P2 (seeFIG. 3) in which the switching valve 14 is opened at a second opening(first degree of valve opening) Vb. As a result, as illustrated in FIG.3, compressed air from the air supply source 78 is supplied to the firstbody port 36 through the supply port 74 and the first port 66 while thecompressed air inside the rod-side cylinder chamber 46 is dischargedfrom the second port 70 through the second exhaust port 82.

Also in the second switch position P2, the opening of the first port 66and the opening of the second port 70 at a predetermined value of thevalve command signal are identical to each other, and the flow rate ofcompressed air supplied to the chuck device 12 through the first port 66(the characteristic curve F1) and the flow rate of compressed airdischarged from the chuck device 12 through the second port 70 (thecharacteristic curve F2) are substantially identical to each other.

This causes the piston 20 of the chuck device 12 to start moving in adirection away from the head cover 40 (in the direction of the arrow B),and as a result, causes the first and second fingers 26 and 28 to startmoving along the rail groove 50 to be separated from each other.

The change in the axial position of the piston 20 is detected by thedetection sensor 32. When the detection sensor 32 detects that thepiston 20 reaches a switch point E, which is a predetermined distance Lshort of a target position D of the piston 20 corresponding to theintermediate position of the first and second fingers 26 and 28, thevalve command signal indicating to open the switching valve 14 at athird opening (third degree of valve opening) Vc is output from thecontroller 16 to the switching valve 14.

The third opening Vc is a degree of opening at which the switching valve14 is switched from the second switch position P2 to the third switchposition P3, and compressed air is supplied from the second body port 38to the rod-side cylinder chamber 46 while the compressed air in thehead-side cylinder chamber 44 is discharged through the first body port36. As illustrated in FIG. 6, the third opening Vc is set closer to thefirst opening Va than a degree of opening at which both the rod side andthe head side are blocked.

After the switching valve 14 is opened at the third opening Vc for apredetermined period t, the switching valve 14 is switched to be openedat a fourth opening (second degree of valve opening) Vd in response tothe updated valve command signal from the controller 16. This causes theswitching valve 14 to be switched to the first switch position P1 (seeFIG. 1) in which the supply and discharge of compressed air to and fromthe first and second body ports 36 and 38 are stopped.

Moreover, the axial position of the piston 20 is input to the controller16 as the position signal, whereby it is determined that the first andsecond fingers 26 and 28 are open and at a standstill in the freelyselected intermediate position.

That is, the switching valve 14 is switched to stop supplying compressedair to the first body port 36 and to supply compressed air to the secondbody port 38 for the predetermined period t before the first and secondfingers 26 and 28 reach the predetermined intermediate position (thetarget position D of the piston 20). As a result, the displacement speedof the piston 20 can be favorably reduced, and the piston 20 can bestopped at the predetermined axial position (the target position D) withhigh precision. Thus, the first and second fingers 26 and 28 can bestopped in the desired intermediate position with high precision.

Moreover, the displacement speed of the first and second fingers 26 and28 is set by the first opening Va and the second opening Vb of theswitching valve 14, and the precision in stopping the first and secondfingers 26 and 28 in the intermediate position is determined by thethird opening Vc, the predetermined distance L to the target position Dof the piston 20 along the axial direction, and the predetermined periodt in which the switching valve 14 is opened at the third opening Vc.

The optimum values of the first opening Va, the second opening Vb, thethird opening Vc, the predetermined distance L to the target position Dof the piston 20, and the predetermined period t vary depending onvarious conditions of the chuck device 12 such as the inner diameter ofthe body hole 34 in the chuck body 18 and the amount of stroke of thepiston 20 along the axial direction, and are stored in the control mapof the controller 16 in advance according to the specifications and thedriving conditions of the chuck device 12.

Moreover, the position of the piston 20 detected by the detection sensor32 is output to the controller 16, and the valve command signal outputto the switching valve 14 is changed based on the axial position and thedisplacement speed of the piston 20 calculated by the controller 16 tochange the valve opening of the switching valve 14 as appropriate. As aresult, opening and closing of the first and second fingers 26 and 28can be controlled more precisely.

Furthermore, as in a drive system 90 illustrated in FIG. 7, the drivesystem may be provided with pressure sensors 92 a and 92 b respectivelycapable of detecting the pressures inside the head-side cylinder chamber44 (the first body port 36) and the rod-side cylinder chamber 46 (thesecond body port 38) in the chuck device 12. At least one of thepressures in the head-side cylinder chamber 44 and the rod-side cylinderchamber 46 respectively detected by the pressure sensors 92 a and 92 bmay be output to the controller 16, and the valve command signal basedon the pressures may be output to the switching valve 14 to set thevalve opening and the switching timing of the switching valve 14.

Yet moreover, as in a drive system 100 illustrated in FIG. 8, the drivesystem may be provided with a differential pressure sensor 102 capableof detecting the difference between the pressure in the head-sidecylinder chamber 44 (the first body port 36) and the pressure in therod-side cylinder chamber 46 (the second body port 38). The pressuredifference detected by the differential pressure sensor 102 may beoutput to the controller 16, and the valve command signal based on thepressure difference may be output to the switching valve 14 to set thevalve opening and the switching timing of the switching valve 14.

In this manner, the drive system 90 provided with the pressure sensors92 a and 92 b and the drive system 100 provided with the differentialpressure sensor 102 can precisely control the opening and closing of thefirst and second fingers 26 and 28 and, at the same time, can favorablyadjust the gripping force of the first and second fingers 26 and 28during gripping of the workpiece based on the pressures detected by thepressure sensors 92 a and 92 b and the pressure difference detected bythe differential pressure sensor 102, respectively.

Moreover, in a case where the volumes of the head-side cylinder chamber44 and the rod-side cylinder chamber 46 of the chuck device 12 arerelatively small, supply and discharge of compressed air need to beswitched quickly in a short time. Thus, for example, a 5-port air servovalve, which directly drives a spool (valve element) in the axialdirection using a linear motor, is the most suitable for the switchingvalve 14.

On the other hand, the switching valve 14 switching the state of supplyof compressed air to the chuck device 12 is not limited to the 5-portservo valve as in the above-described drive systems 10, 90, and 100. Forexample, as in a drive system 110 illustrated in FIG. 9, the drivesystem may be provided with a pair of switching valves 112 a and 112 b,which are 3-port servo valves, and an output port 114 a of the switchingvalve 112 a may be connected to the first body port 36 of the chuckdevice 12 while an output port 114 b of the switching valve 112 b may beconnected to the second body port 38 of the chuck device 12.

To change the chuck device 12 to the open state in the drive system 110,compressed air is supplied from the switching valve 112 a to the firstbody port 36 while compressed air is discharged from the chuck device 12to the outside through the switching valve 112 b. This causes the firstand second fingers 26 and 28 to enter the release state (open) under theeffect of displacement of the piston 20.

On the other hand, to change the chuck device 12 to the closed state,compressed air is supplied from the switching valve 112 b to the secondbody port 38 while compressed air is discharged from the chuck device 12to the outside through the switching valve 112 a. This causes the firstand second fingers 26 and 28 to enter the gripping state (closed) underthe effect of displacement of the piston 20.

Moreover, the first and second fingers 26 and 28 can also be stopped ata freely selected intermediate position by switching the state of supplyof compressed air to the chuck device 12 as appropriate using theswitching valves 112 a and 112 b.

The drive systems 10, 90, 100, and 110 and the control methods for thechuck device 12 according to the present invention are not limited inparticular to the embodiments described above, and may have variousconfigurations without departing from the scope of the present inventionas a matter of course.

What is claimed is:
 1. A drive system for driving a chuck deviceincluding a piston displaceable in an axial direction under an effect ofsupply of fluid and a pair of fingers configured to be opened and closedaccording to the displacement of the piston, the drive systemcomprising: a controller; a detection sensor configured to detect anaxial position of the piston; and a switching valve configured to switcha state of supply of the fluid to the chuck device, wherein theswitching valve is a servo valve, of which degree of valve opening iscontrollable based on a control signal input from the controller, and anamount of displacement of the piston and an amount of opening andclosing of the fingers are controlled by changing the degree of valveopening.
 2. The drive system according to claim 1, wherein the switchingvalve is a 5-port servo valve including a first port connected to afirst cylinder chamber of the chuck device, and a second port connectedto a second cylinder chamber of the chuck device.
 3. The drive systemaccording to claim 1, wherein: the switching valve includes a pair of3-port servo valves; and one of the 3-port servo valves is connected toa first cylinder chamber of the chuck device, and another of the 3-portservo valves is connected to a second cylinder chamber of the chuckdevice.
 4. The drive system according to claim 2, further comprising: apressure sensor provided for at least one of the first cylinder chamberand the second cylinder chamber and configured to detect a pressure inthe cylinder chamber.
 5. The drive system according to claim 2, furthercomprising: a pressure sensor configured to detect a difference betweena pressure in the first cylinder chamber and a pressure in the secondcylinder chamber.
 6. The drive system according to claim 2, wherein the5-port servo valve is a direct acting valve that includes a drive sourceconfigured to perform driving by an electrical signal, and that isconfigured to switch the state of supply of the fluid under an effect ofdrive of the drive source.
 7. The drive system according to claim 6,wherein the 5-port servo valve switches a state of supply and dischargeof the fluid and changes the degree of valve opening.
 8. A controlmethod of controlling the chuck device according to claim 1, the controlmethod comprising the steps of: opening or closing the fingers byopening the switching valve at a first degree of valve opening to supplythe fluid to a first cylinder chamber of the chuck device and todischarge the fluid from a second cylinder chamber of the chuck deviceso that the piston moves in one direction; and stopping the fingers inan intermediate position between a fully open position and a fullyclosed position by opening the switching valve at a second degree ofvalve opening to stop supplying the fluid to the first cylinder chamberand to stop discharging the fluid from the second cylinder chamber whenthe axial position of the piston reaches a target position set inadvance while the fingers are being opened or closed.
 9. The controlmethod according to claim 8, wherein the switching valve is opened at athird degree of valve opening to supply the fluid to the second cylinderchamber at a point before the axial position of the piston reaches thetarget position while the fingers are being opened or closed.
 10. Thecontrol method according to claim 9, wherein the switching valve isopened at the third degree of valve opening for a predetermined periodand then switched to be opened at the second degree of valve opening.